Microporous Material

ABSTRACT

Microporous materials that include thermoplastic organic polyolefin polymer (e.g., ultrahigh molecular weight polyolefin, such as polyethylene), particulate filler (e.g., precipitated silica), and a network of interconnecting pores, are described. The microporous materials of the present invention possess controlled volatile material transfer properties. The microporous materials can have a density of at least 0.8 g/cm 3 ; and a volatile material transfer rate, from the volatile material contact surface to the vapor release surface of the microporous material, of from 0.04 to 0.6 mg/(hour*cm 2 ). In addition, when volatile material is transferred from the volatile material contact surface to the vapor release surface, the vapor release surface is substantially free of volatile material in liquid form.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/045,824, filed Oct. 4, 2013, now U.S. Pat. No. 9,861,719, issued Jan.9, 2018, which is a continuation-in-part of U.S. patent application Ser.No. 13/473,001, filed May 16, 2012, now abandoned, which is acontinuation of U.S. patent application Ser. No. 12/761,020, filed Apr.15, 2010, now U.S. Pat. No. 8,435,631, issued May 7, 2013, all of whichare incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to microporous materials that possesscontrolled volatile material transfer properties. The microporousmaterial includes thermoplastic organic polymer, particulate filler, anda network of interconnecting pores.

BACKGROUND OF THE INVENTION

The delivery of volatile materials, such as fragrances, e.g., airfresheners, may be achieved by means of a delivery apparatus thatincludes a reservoir containing volatile material. The deliveryapparatus or delivery device typically includes a vapor permeablemembrane that covers or encloses the reservoir. Volatile material withinthe reservoir passes through the vapor permeable membrane and isreleased into the atmosphere, e.g., air, on the atmospheric side of themembrane. Vapor permeable membranes are typically fabricated fromorganic polymers and are porous.

The rate at which volatile material passes through the vapor permeablemembrane is generally an important factor. For example, if the rate atwhich volatile material passes through the vapor permeable membrane istoo low, properties associated with the volatile material, such asfragrance, will typically be undesirably low or imperceptible. If, onthe other hand, the rate at which volatile material passes through thevapor permeable membrane is too high, the reservoir of volatile materialmay be depleted too quickly, and properties associated with the volatilematerial, such as fragrance, may be undesirably high or in someinstances overpowering.

It is also generally desirable to minimize or prevent the formation ofliquid volatile material on the atmospheric or exterior side of thevapor permeable membrane, from which the volatile material is releasedinto the atmosphere, e.g., into the air. Liquid volatile material thatpasses through the exterior side of the vapor permeable membrane maycollect, e.g., puddle, within or on the exterior side of the membraneand leak from the delivery device resulting in, for example, staining ofarticles, such as clothing or furniture, that come into contact with theliquid volatile material. In addition, the formation of liquid volatilematerial on the exterior side of the vapor permeable membrane may resultin the uneven release of volatile material from the delivery device.

Further increases in ambient temperature may increase the rate at whichvolatile material passes through the vapor permeable membrane toundesirably high rates. For example, a delivery device that is usedwithin the passenger compartment of an automobile may be exposed toincreases in ambient temperature. As such, minimizing the increase inthe rate at which volatile material contained within the device passesthrough the vapor permeable membrane, as a function of increasingambient temperature, is typically desirable.

It would be desirable to develop new microporous materials that possesscontrolled volatile material transfer properties. It would be furtherdesirable that when such newly developed microporous materials are usedas a vapor permeable membrane in a delivery device, the microporousmaterial minimizes the formation of liquid volatile material on theexterior side or surface of the membrane. In addition, the rate at whichvolatile material passes through such microporous materials shouldincrease minimally with increases in ambient temperature.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided, amicroporous material comprising:

(a) a matrix of substantially water-insoluble thermoplastic organicpolymer comprising polyolefin;

(b) finely divided, substantially water-insoluble particulate filler,said particulate filler being distributed throughout said matrix andconstituting from 40 to 90 percent by weight, based on the total weightof said microporous material; and

(c) a network of interconnecting pores communicating substantiallythroughout said microporous material;

wherein said microporous material has

-   -   a density of at least 0.8 g/cm³,    -   a volatile material contact surface,    -   a vapor release surface, wherein said volatile material contact        surface and said vapor release surface are substantially opposed        to each other, and    -   a volatile material transfer rate from said volatile material        contact surface to said vapor release surface of from 0.04 to        0.6 mg/(hour*cm²), and

wherein when volatile material is transferred from said volatilematerial contact surface to said vapor release surface (at a volatilematerial transfer rate of from 0.04 to 0.6 mg/(hour*cm²)), said vaporrelease surface is substantially free of volatile material in liquidform.

Further, the present invention provides a microporous materialcomprising:

(a) a matrix of substantially water-insoluble thermoplastic organicpolymer comprising polyolefin;

(b) finely divided, substantially water-insoluble particulate filler,said particulate filler being distributed throughout said matrix andconstituting from 40 to 90 percent by weight, based on the total weightof said microporous material; and

(c) a network of interconnecting pores communicating substantiallythroughout said microporous material;

wherein said microporous material has

-   -   a density of less than 0.8 g/cm³,    -   a volatile material contact surface,    -   a vapor release surface, wherein said volatile material contact        surface and said vapor release surface are substantially opposed        to each other, wherein (i) at least a portion of said volatile        material contact surface has a first coating thereon,        and/or (ii) at least a portion of said vapor release surface has        a second coating thereon,    -   a volatile material transfer rate from said volatile material        contact surface to said vapor release surface of from 0.04 to        0.6 mg/(hour*cm²), and

wherein when volatile material is transferred from said volatilematerial contact surface to said vapor release surface (at a volatilematerial transfer rate of from 0.04 to 0.6 mg/(hour*cm²)), said vaporrelease surface is substantially free of volatile material in liquidform.

Also, the present invention provides, a microporous material comprising:

(a) a matrix of substantially water-insoluble thermoplastic organicpolymer comprising polyolefin;

(b) finely divided, substantially water-insoluble particulate filler,said particulate filler being distributed throughout said matrix andconstituting from 40 to 90 percent by weight, based on the total weightof said microporous material; and

(c) a network of interconnecting pores communicating substantiallythroughout said microporous material;

wherein said microporous material has,

-   -   a volatile material contact surface,    -   a vapor release surface, wherein said volatile material contact        surface and said vapor release surface are substantially opposed        to each other, wherein (i) at least a portion of said volatile        material contact surface has a first coating thereon,        and/or (ii) at least a portion of said vapor release surface has        a second coating thereon, wherein said first coating and said        second coating are each independently selected from a coating        composition comprising poly(vinyl alcohol), and    -   a volatile material transfer rate, from said volatile material        contact surface to said vapor release surface, of at least 0.04        mg/(hour*cm²), and

wherein when said microporous material, i.e., the poly(vinyl alcoholcoated microporous material, is exposed to a temperature increase offrom 25° C. to 60° C., said volatile material transfer rate increases byless than or equal to 150 percent.

DETAILED DESCRIPTION OF THE INVENTION

As used herein and in the claims, the term “volatile material contactsurface” means that surface of the microporous material that faces and,typically, is in contact with the volatile material, which is, forexample, contained in a reservoir, as described in further detail below.

As used herein and in the claims, the term “vapor release surface” meansthat surface of the microporous material that does not face and/orcontact directly the volatile material, and from which surface volatilematerial is released into an exterior atmosphere in a gaseous or vaporform.

As used herein and in the claims, the term “(meth)acrylate” and similarterms, such as “esters of (meth)acrylic acid”, means acrylates and/ormethacrylates.

As used herein and in the claims, the “volatile material transfer rate”of the microporous materials was determined in accordance with thefollowing description. A test reservoir, having an interior volumesufficient to contain 2 milliliters of volatile material, such as benzylacetate, was fabricated from a clear thermoplastic polymer. The interiordimensions of the reservoir was defined by a circular diameter at theedge of the open face of approximately 4 centimeters and a depth of nogreater than 1 centimeter. The open face was used to determine thevolatile material transfer rate. With the test reservoir laying flat(with the open face facing upward), about 2 milliliters of benzylacetate was introduced into the test reservoir. With benzyl acetateintroduced into the test reservoir, a sheet of microporous materialhaving a thickness of from 6 to 18 mils was placed over the openface/side of the test reservoir, such that 12.5 cm² of the volatilematerial contact surface of the microporous sheet was exposed to theinterior of the reservoir. The test reservoir was weighed to obtain aninitial weight of the entire charged assembly. The test reservoir,containing benzyl acetate and enclosed with the sheet of microporousmaterial, was then placed, standing upright, in a laboratory chemicalfume hood having approximate dimensions of 5 feet [1.52 meters](height)×5 feet [1.52 meters] (width)×2 feet [0.61 meters] (depth). Withthe test reservoir standing upright, benzyl acetate was in directcontact with at least a portion of the volatile material contact surfaceof the microporous sheet. The glass doors of the fume hood were pulleddown, and the air flow through the hood was adjusted so as to have eight(8) turns (or turnovers) of hood volume per hour. Unless otherwiseindicated, the temperature in the hood was maintained at 25° C.±5° C.The humidity within in the fume hood was ambient. The test reservoirswere regularly weighed in the hood. The calculated weight loss of benzylacetate, in combination with the elapsed time and surface area of themicroporous sheet exposed to the interior of the test reservoir, wereused to determine the volatile transfer rate of the microporous sheet,in units of mg/(hour*cm²).

As used herein and in the claims, the percent increase in the volatilematerial transfer rate of the microporous material of the presentinvention from 25° C. to 60° C. was determined for separate butsubstantially equivalent microporous material sheet samples at 25° C.and 60° C., in accordance with the method described above. Reservoirswere placed in a large glass bell jar and over a 50% aqueous solution ofpotassium chloride also contained in the bell jar. The entire bell jarwith contents was placed in an oven heated to 60° C. The reservoirs wereheld under these conditions for a period of 7 to 10 hours. Thereservoirs were then returned to the hood at ambient conditionsovernight and the process was repeated over several days. Each of thereservoirs was weighed before being placed in the bell jar and afterbeing removed from the bell jar. Upon removal from the bell jar, theweight of each reservoir was taken after the reservoir had returned toambient temperature.

As used herein and in the claims, the following method was used todetermine if the vapor release surface of the microporous material is“substantially free of volatile material in liquid form”. When the testreservoirs were weighed, as described above, the vapor release surfaceof the microporous sheet was examined visually by naked eye to determineif drops and/or a film of liquid were present thereon. If any evidenceof drops (i.e., a single drop) and/or a film of liquid was visuallyobserved on the vapor release surface, but did not run off the surface,the microporous sheet was considered to be acceptable. If the drops ofvolatile material liquid ran off the vapor release surface, themicroporous sheet was determined to have failed. If no evidence of drops(i.e., not one drop) and/or a film of liquid was visually observed onthe vapor release surface, the microporous sheet was determined to besubstantially free of volatile material in liquid form.

Unless otherwise indicated, all ranges disclosed herein are to beunderstood to encompass any and all sub-ranges subsumed therein. Forexample, a stated range of “1 to 10” should be considered to include anyand all sub-ranges between (and inclusive of) the minimum value of 1 andthe maximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less, e.g.,1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in its respective testing measurement,including that found in the measuring instrument.

Unless otherwise indicated, all numbers or expressions, such as thoseexpressing structural dimensions, quantities of ingredients, etc., asused in the specification and claims, are understood as modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in this specification andattached claims are approximations that can vary depending upon thedesired results sought to be obtained by the present invention. At thevery least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques. Further, as used in this specification and the attachedclaims, the singular forms “a”, “an” and “the” are intended to includeplural referents, unless expressly and unequivocally limited to onereferent.

The term “volatile material”, as used herein and in the claims, means amaterial that is capable of conversion to a gaseous or vapor form, i.e.,capable of vaporizing, at ambient room temperature and pressure, and inthe absence of imparted additional or supplementary energy, e.g., in theform of heat and/or agitation. The volatile material can comprise anorganic volatile material, which can include those volatile materialscomprising a solvent-based material, or those which are dispersed in asolvent-based material. The volatile material may be in a liquid formand/or in a solid form, and may be naturally occurring or syntheticallyformed. When in a solid form, the volatile material typically sublimesfrom the solid form to the vapor form without passing thru anintermediate liquid form. The volatile material may optionally becombined or formulated with nonvolatile materials, such as a carrier,e.g., water and/or nonvolatile solvents. In the case of a solid volatilematerial, the nonvolatile carrier may be in the form of a porousmaterial, e.g., a porous inorganic material, in which the solid volatilematerial is held. Also, the solid volatile material may be in the formof a semi-solid gel.

The volatile material may be a fragrance material, such as a naturallyoccurring or synthetic perfume oil. Examples of perfume oils from whichthe liquid volatile material may be selected include, but are notlimited to, oil of bergamot, bitter orange, lemon, mandarin, caraway,cedar leaf, clove leaf, cedar wood, geranium, lavender, orange,origanum, petitgrain, white cedar, patchouli, neroili, rose absolute,and combinations thereof. Examples of solid fragrance materials fromwhich the volatile material may be selected include, but are not limitedto, vanillin, ethyl vanillin, coumarin, tonalid, calone, heliotropene,musk xylol, cedrol, musk ketone benzophenone, raspberry ketone, methylnaphthyl ketone beta, phenyl ethyl salicylate, veltol, maltol, maplelactone, proeugenol acetate, evemyl, and combinations thereof.

The volatile material transfer rate of the microporous material can beless than or equal to 0.7 mg/(hour*cm²), or less than or equal to 0.6mg/(hour*cm²), or less than or equal to 0.55 mg/(hour*cm²), or less thanor equal to 0.50 mg/(hour*cm²). The volatile material transfer rate ofthe microporous material can be equal to or greater than 0.02mg/(hour*cm²), or equal to or greater than 0.04 mg/(hour*cm²), or equalto or greater than 0.30 mg/(hour*cm²), or equal to or greater than 0.35mg/(hour*cm²). The volatile material transfer rate of the microporousmaterial may range between any combination of these upper and lowervalues. For example, the volatile material transfer rate of themicroporous material can be from 0.04 to 0.6 mg/(hour*cm²), or from 0.2to 0.6 mg/(hour*cm²), or from 0.30 to 0.55 mg/(hour*cm²), or from 0.35to 0.50 mg/(hour*cm²), in each case inclusive of the recited values.

While not intending to be bound by any theory, when volatile material istransferred from the volatile material contact surface to the vaporrelease surface of the microporous material, it is believed that thevolatile material is in a form selected from liquid, vapor and acombination thereof. In addition, and without intending to be bound byany theory, it is believed that the volatile material, at least in part,moves through the network of interconnecting pores that communicatesubstantially throughout the microporous material. Typically, thetransfer of volatile material occurs at temperatures of from 15° C. to40° C., e.g., from 15° C. or 18° C. to 30° C. or 35° C. and at ambientatmospheric pressure.

The microporous material can have a density of at least 0.7 g/cm³′ or atleast 0.8 g/cm³. As used herein and in the claims, the density of themicroporous material is determined by measuring the weight and volume ofa sample of the microporous material. The upper limit of the density ofthe microporous material may range widely, provided it has a targetedvolatile material transfer rate of, for example, from 0.04 to 0.6mg/(hour*cm²), and the vapor release surface is substantially free ofvolatile material in liquid form when volatile material is transferredfrom the volatile material contact surface to said vapor releasesurface. Typically, the density of the microporous material is less thanor equal to 1.5 g/cm³, or less than or equal to 1.0 g/cm³. The densityof the microporous material can range between any of the above-statedvalues, inclusive of the recited values. For example, the microporousmaterial can have a density of from 0.7 g/cm³ to 1.5 g/cm³, such as,from 0.8 g/cm³ to 1.2 g/cm³, inclusive of the recited values.

When the microporous material has a density of at least 0.7 g/cm³, suchas at least 0.8 g/cm³, the volatile material contact surface and thevapor release surface of the microporous material each may be free of acoating material thereon. When free of a coating material thereon, thevolatile material contact surface and the vapor release surface each aredefined by the microporous material.

When the microporous material has a density of at least 0.7 g/cm³, suchas at least 0.8 g/cm³, at least a portion of the volatile materialcontact surface of the microporous material optionally may have a firstcoating thereon, and/or at least a portion of the vapor release surfaceof the microporous material optionally may have a second coatingthereon. The first coating and the second coating may be the same ordifferent. When at least a portion of the volatile material contactsurface has a first coating thereon, the volatile material contactsurface is defined at least in part by the first coating. When at leasta portion of the vapor release surface has a second coating thereon, thevapor release surface is defined at least in part by the second coating.

The first coating and the second coating may each be formed from acoating selected from liquid coatings and solid particulate coatings(e.g., powder coatings). Typically, the first and second coatings eachindependently are formed from a coating selected from liquid coatings,which may optionally include a solvent selected from water, organicsolvents and combinations thereof. The first and second coatings eachindependently may be selected from crosslinkable coatings, e.g.,thermosetting coatings and photo-curable coatings, and non-crosslinkablecoatings, e.g., air-dry coatings. The first and second coatings may beapplied to the respective surfaces of the microporous material inaccordance with art-recognized methods, such as spray application,curtain coating, dip coating, and/or drawn-down coating, e.g., by meansof a doctor blade or draw-down bar, techniques.

The first and second coating compositions each independently canoptionally include art-recognized additives, such as antioxidants,ultraviolet light stabilizers, flow control agents, dispersionstabilizers, e.g., in the case of aqueous dispersions, and colorants,e.g., dyes and/or pigments. Typically, the first and second coatingcompositions are free of colorants, and as such are substantially clearor opaque. Optional additives may be present in the coating compositionsin individual amounts of from, for example, 0.01 to 10 percent byweight, based on the total weight of the coating composition.

The first coating and said second coating each independently can beformed from an aqueous coating composition that includes dispersedorganic polymeric material. The aqueous coating composition may have aparticle size of from 200 to 400 nm. The solids of the aqueous coatingcomposition may vary widely, for example from 0.1 to 30 percent byweight, or from 1 to 20 percent by weight, in each case based on totalweight of the aqueous coating composition. The organic polymerscomprising the aqueous coating compositions may have number averagemolecular weights (Mn) of, for example, from 1000 to 4,000,000, or from10,000 to 2,000,000.

The aqueous coating composition can be selected from aqueouspoly(meth)acrylate dispersions, aqueous polyurethane dispersions,aqueous silicone (or silicon) oil dispersions, and combinations thereof.The poly(meth)acrylate polymers of the aqueous poly(meth)acrylatedispersions may be prepared in accordance with art-recognized methods.For example, the poly(meth)acrylate polymers may include residues (ormonomer units) of alkyl (meth)acrylates having from 1 to 20 carbon atomsin the alkyl group. Examples of alkyl (meth)acrylates having from 1 to20 carbon atoms in the alkyl group include, but are not limited to,methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, propyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate,tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl(meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, and3,3,5-trimethylcyclohexyl (meth)acrylate. For purposes of non-limitingillustration, an example of an aqueous poly(meth)acrylate dispersionfrom which the first and second coating compositions may each beindependently selected is HYCAR 26138, which is commercially availablefrom Lubrizol Advanced Materials, Inc.

The polyurethane polymers of the aqueous polyurethane dispersions, fromwhich the first and second coatings each independently may be selected,include any of those known to the skilled artisan. Typically thepolyurethane polymers are prepared from isocyanate functional materialshaving two or more isocyanate groups, and active hydrogen functionalmaterials having two or more active hydrogen groups. The active hydrogengroups may be selected from, for example, hydroxyl groups, thiol groups,primary amines, secondary amines, and combinations thereof. For purposesof non-limiting illustration, an example of an aqueous polyurethanedispersion from which the first and second coating compositions may eachbe independently selected is WITCOBOND W-240, which is commerciallyavailable from Chemtura Corporation.

The silicon polymers of the aqueous silicone oil dispersions may beselected from known and art-recognized aqueous silicone oil dispersions.For purposes of non-limiting illustration, an example of an aqueoussilicon dispersion from which the first and second coating compositionsmay each be independently selected is MOMENTIVE LE-410, which iscommercially available from Momentive Performance Materials.

The first coating and the second coating each independently can beapplied at any suitable thickness, provided the microporous material hasa targeted volatile material transfer rate of, for example, from 0.04 to0.6 mg/(hour*cm²), and the vapor release surface is substantially freeof volatile material in liquid form when volatile material istransferred from the volatile material contact surface to said vaporrelease surface. Also, the first coating and the second coating eachindependently can have a coating weight, i.e., the weight of the coatingwhich is on the microporous material, of from 0.01 to 5.5 g/m², such asfrom 0.1 to 5.0 g/m², or from 0.5 to 3 g/m², or from 0.75 to 2.5 g/m²,or from 1 to 2 g/m².

The microporous material can have a density of less than 0.8 g/cm³, andat least a portion of the volatile material contact surface of themicroporous material can have a first coating thereon, and/or at least aportion of the vapor release surface of the microporous material canhave a second coating thereon. The first coating and the second coatingmay be the same or different, and are each independently as describedpreviously herein with regard to the optional first and second coatingsof the microporous material having a density of at least 0.8 g/cm³.

When less than 0.8 g/cm³, the density of the microporous material of thepresent invention may have any suitable lower limit, provided themicroporous material has a targeted volatile material transfer rate of,for example, from 0.04 to 0.6 mg/(hour*cm²), and the vapor releasesurface is substantially free of volatile material in liquid form whenvolatile material is transferred from the volatile material contactsurface to said vapor release surface. With this particular embodimentof the present invention, the density of the microporous material may befrom 0.6 to less than 0.8 g/cm³, or from 0.6 to 0.75 g/cm³, e.g., from0.60 to 0.75 g/cm³, or from 0.6 to 0.7 g/cm³, e.g., from 0.60 to 0.70g/cm³, or from 0.65 to 0.70 g/cm³.

Further, at least a portion of the volatile material contact surface ofthe microporous material can have a first coating thereon, and/or atleast a portion of the vapor release surface of the microporous materialcan have a second coating thereon, in which the first and secondcoatings each independently are selected from a coating compositioncomprising a poly(vinyl alcohol).

With the poly(vinyl alcohol) coated embodiment of the present invention,when the microporous material, i.e., the poly(vinyl alcohol) coatedmicroporous material, is exposed to a temperature increase of from 25°C. to 60° C., the volatile material transfer rate thereof increases byless than or equal 150 percent. When the poly(vinyl alcohol) coatedmicroporous material is exposed to a temperature increase, e.g., from anambient temperature of from 25° C. to 60° C., the volatile materialtransfer rate typically increases, and typically does not decreaseunless, for example, the microporous material has been damaged byexposure to the higher ambient temperature. As such, and as used hereinand in the claims, the statement “the volatile material transfer ratethereof increases by less than or equal to [a stated] percent”, e.g.,150 percent, is inclusive of a lower limit of 0 percent, but is notinclusive of a lower limit that is less than 0 percent.

For purposes of illustration, when the poly(vinyl alcohol) coatedmicroporous material has a volatile material transfer rate of 0.3mg/(hour*cm²) at 25° C., and when the microporous material is exposed toa temperature of 60° C., the volatile material transfer rate increasesto a value that is less than or equal to 0.75 mg/(hour*cm²).

In an embodiment when the microporous material, i.e., the poly(vinylalcohol) coated microporous material, is exposed to a temperatureincrease of from 25° C. to 60° C., the volatile material transfer ratethereof increases by less than or equal to 125 percent. For example,when the poly(vinyl alcohol) coated microporous material has a volatilematerial transfer rate of 0.3 mg/(hour*cm²) at 25° C., and when themicroporous material is exposed to a temperature of 60° C., the volatilematerial transfer rate increases to a value that is less than or equalto 0.68 mg/(hour*cm²).

Further, when the microporous material, i.e., the poly(vinyl alcohol)coated microporous material, is exposed to a temperature increase offrom 25° C. to 60° C., the volatile material transfer rate thereofincreases by less than or equal 100 percent. For example, when thepoly(vinyl alcohol) coated microporous material has a volatile materialtransfer rate of 0.3 mg/(hour*cm²) at 25° C., and when the microporousmaterial is exposed to a temperature of 60° C., the volatile materialtransfer rate increases to a value that is less than or equal to 0.6mg/(hour*cm²).

The first and second poly(vinyl alcohol) coatings may each beindependently present in any suitable coating weight, provided themicroporous material has a targeted volatile material transfer rate of,for example, at least 0.04 mg/(hour*cm²), and when the microporousmaterial, i.e., the poly(vinyl alcohol) coated microporous material, isexposed to a temperature increase of from 25° C. to 60° C., the volatilematerial transfer rate thereof increases by less than or equal to 150percent. Typically, the first poly(vinyl alcohol) coating and the secondpoly(vinyl alcohol) coating each independently have a coating weight offrom 0.01 to 5.5 g/m², or from 0.1 to 4.0 g/m², or from 0.5 to 3.0 g/m²,or from 0.75 to 2.0 g/m².

The volatile material transfer rate of the poly(vinyl alcohol) coatedmicroporous material can be at least 0.02 mg/(hour*cm²). The volatilematerial transfer rate of the poly(vinyl alcohol) coated microporousmaterial may be equal to or greater than 0.04 mg/(hour*cm²), or equal toor greater than 0.1 mg/(hour*cm²), or equal to or greater than 0.2mg/(hour*cm²), or equal to or greater than 0.30 mg/(hour*cm²), or equalto or greater than 0.35 mg/(hour*cm²). The volatile material transferrate of the poly(vinyl alcohol) coated microporous material may be lessthan or equal to 0.7 mg/(hour*cm²), or less than or equal to 0.6mg/(hour*cm²), or less than or equal to 0.55 mg/(hour*cm²), or less thanor equal to 0.50 mg/(hour*cm²). The volatile material transfer rate ofthe poly(vinyl alcohol) coated microporous material may range betweenany combination of these upper and lower values, inclusive of therecited values. For example, the volatile material transfer rate of thepoly(vinyl alcohol) coated microporous material can be at least 0.02mg/(hour*cm²), such as from 0.04 to 0.70 mg/(hour*cm²), or from 0.04 to0.60 mg/(hour*cm²), or from 0.20 to 0.60 mg/(hour*cm²), or from 0.30 to0.55 mg/(hour*cm²), or from 0.35 to 0.50 mg/(hour*cm²), in each caseinclusive of the recited values.

The density of the microporous material of the poly(vinyl alcohol)coated microporous material embodiment of the present invention may varywidely, provided that the poly(vinyl alcohol) coated microporousmaterial has a targeted volatile material transfer rate, for example, ofat least 0.04 mg/(hour*cm²), and when the microporous material, i.e.,the poly(vinyl alcohol) coated microporous material, is exposed to atemperature increase of from 25° C. to 60° C., the volatile materialtransfer rate thereof increases by less than or equal to 150 percent.

Further, the density of the microporous material, of the poly(vinylalcohol) coated microporous material, may be at least 0.7 g/cm³, such asat least 0.8 g/cm³, e.g., from 0.8 to 1.2 g/cm³, all inclusive of therecited values. In an embodiment of the present invention, the densityof the poly(vinyl alcohol) coated microporous material, i.e., thedensity of the microporous material prior to application of thepoly(vinyl alcohol) coating, is less than 0.8 g/cm³. For example, thedensity of the microporous material, of the poly(vinyl alcohol) coatedmicroporous material, may be from 0.6 to less than 0.8 g/cm³, or from0.6 to 0.75 g/cm³, e.g., from 0.60 to 0.75 g/cm³, or from 0.6 to 0.7g/cm³, e.g., from 0.60 to 0.70 g/cm³, or from 0.65 to 0.70 g/cm³, allinclusive of the recited values.

With regard to the poly(vinyl alcohol) coated microporous material ofthe present invention, when volatile material is transferred from thevolatile material contact surface to the vapor release surface, thevapor release surface is substantially free of volatile material inliquid form.

The poly(vinyl alcohol) coating may be selected from liquid coatingswhich may optionally include a solvent selected from water, organicsolvents and combinations thereof. The poly(vinyl alcohol) coating maybe selected from crosslinkable coatings, e.g., thermosetting coatings,and non-crosslinkable coatings, e.g., air-dry coatings. The poly(vinylalcohol) coating may be applied to the respective surfaces of themicroporous material in accordance with art-recognized methods, such asspray application, curtain coating, or drawn-down coating, e.g., bymeans of a doctor blade or draw-down bar.

In an embodiment, the first and second poly(vinyl alcohol) coatings areeach independently formed from aqueous poly(vinyl alcohol) coatingcompositions. The solids of the aqueous poly(vinyl alcohol) coatingcomposition may vary widely, for example from 0.1 to 15 percent byweight, or from 0.5 to 9 percent by weight, in each case based on totalweight of the aqueous coating composition. The poly(vinyl alcohol)polymer of the poly(vinyl alcohol) coating compositions may have numberaverage molecular weights (Mn) of, for example, from 100 to 1,000,000,or from 1000 to 750,000.

The poly(vinyl alcohol) polymer of the poly(vinyl alcohol) coatingcomposition may be a homopolymer or copolymer. Comonomers from which thepoly(vinyl alcohol) copolymer may be prepared include those which arecopolymerizable (by means of radical polymerization) with vinyl acetate,and which are known to the skilled artisan. For purposes ofillustration, comonomers from which the poly(vinyl alcohol) copolymermay be prepared include, but are not limited to: (meth)acrylic acid,maleic acid, fumaric acid, crotonic acid, metal salts thereof, alkylesters thereof, e.g., C₂-C₁₀ alkyl esters thereof, polyethylene glycolesters thereof, and polypropylene glycol esters thereof; vinyl chloride;tetrafluoroethylene; 2-acrylamido-2-methyl-propane sulfonic acid and itssalts; acrylamide; N-alkyl acrylamide; N,N-dialkyl substitutedacrylamides; and N-vinyl formamide.

For purposes of non-limiting illustration, an example of a poly(vinylalcohol) coating composition that may be used to form the poly(vinylalcohol) coated microporous material of the present invention is CELVOL325, which is commercially available from Sekisui Specialty Chemicals.

The first and second poly(vinyl alcohol) coating compositions may eachindependently include art-recognized additives, such as antioxidants,ultraviolet light stabilizers, flow control agents, dispersionstabilizers, e.g., in the case of aqueous dispersions, and colorants,e.g., dyes and/or pigments. Typically, the first and second poly(vinylalcohol) coating compositions are free of colorants, and are as suchsubstantially clear or opaque. Optional additives may be present in thepoly(vinyl alcohol) coating compositions in individual amounts of from,for example, 0.01 to 10 percent by weight, based on the total weight ofthe coating composition.

The matrix of the microporous material is composed of substantiallywater-insoluble thermoplastic organic polymer. The numbers and kinds ofsuch polymers suitable for use as the matrix are large. In general, anysubstantially water-insoluble thermoplastic organic polymer which can beextruded, calendered, pressed, or rolled into film, sheet, strip, or webmay be used. The polymer may be a single polymer or it may be a mixtureof polymers. The polymers may be homopolymers, copolymers, randomcopolymers, block copolymers, graft copolymers, atactic polymers,isotactic polymers, syndiotactic polymers, linear polymers, or branchedpolymers. When mixtures of polymers are used, the mixture may behomogeneous or it may comprise two or more polymeric phases.

Examples of classes of suitable substantially water-insolublethermoplastic organic polymers include thermoplastic polyolefins,poly(halo-substituted olefins), polyesters, polyamides, polyurethanes,polyureas, poly(vinyl halides), poly(vinylidene halides), polystyrenes,poly(vinyl esters), polycarbonates, polyethers, polysulfides,polyimides, polysilanes, polysiloxanes, polycaprolactones,polyacrylates, and polymethacrylates. Contemplated hybrid classes, fromwhich the substantially water-insoluble thermoplastic organic polymersmay be selected include, for example, thermoplasticpoly(urethane-ureas), poly(ester-amides), poly(silane-siloxanes), andpoly(ether-esters. Further examples of suitable substantiallywater-insoluble thermoplastic organic polymers include thermoplastichigh density polyethylene, low density polyethylene, ultrahigh molecularweight polyethylene, polypropylene (atactic, isotactic, orsyndiotactic), poly(vinyl chloride), polytetrafluoroethylene, copolymersof ethylene and acrylic acid, copolymers of ethylene and methacrylicacid, poly(vinylidene chloride), copolymers of vinylidene chloride andvinyl acetate, copolymers of vinylidene chloride and vinyl chloride,copolymers of ethylene and propylene, copolymers of ethylene and butene,poly(vinyl acetate), polystyrene, poly(omega-aminoundecanoic acid)poly(hexamethylene adipamide), poly(epsilon-caprolactam), andpoly(methyl methacrylate). The recitation of these classes and exampleof substantially water-insoluble thermoplastic organic polymers is notexhaustive, and are provided only for purposes of illustration.

Substantially water-insoluble thermoplastic organic polymers may inparticular include, for example, poly(vinyl chloride), copolymers ofvinyl chloride, or mixtures thereof. In an embodiment, thewater-insoluble thermoplastic organic polymer includes an ultrahighmolecular weight polyolefin selected from: ultrahigh molecular weightpolyolefin, e.g., essentially linear ultrahigh molecular weightpolyolefin) having an intrinsic viscosity of at least 10deciliters/gram; or ultrahigh molecular weight polypropylene, e.g.,essentially linear ultrahigh molecular weight polypropylene) having anintrinsic viscosity of at least 6 deciliters/gram; or mixtures thereof.In a particular embodiment, the water-insoluble thermoplastic organicpolymer includes ultrahigh molecular weight polyethylene, e.g., linearultrahigh molecular weight polyethylene, having an intrinsic viscosityof at least 18 deciliters/gram.

Ultrahigh molecular weight polyethylene (UHMWPE) is not a thermosetpolymer having an infinite molecular weight, but is technicallyclassified as a thermoplastic. However, because the molecules aresubstantially very long chains, UHMWPE softens when heated but does notflow as a molten liquid in a normal thermoplastic manner. The very longchains and the peculiar properties they provide to UHMWPE are believedto contribute in large measure to the desirable properties ofmicroporous materials made using this polymer.

As indicated earlier, the intrinsic viscosity of the UHMWPE is at leastabout 10 deciliters/gram. Usually the intrinsic viscosity is at leastabout 14 deciliters/gram. Often the intrinsic viscosity is at leastabout 18 deciliters/gram. In many cases the intrinsic viscosity is atleast about 19 deciliters/gram. Although there is no particularrestriction on the upper limit of the intrinsic viscosity, the intrinsicviscosity is frequently in the range of from about 10 to about 39deciliters/gram, e.g., in the range of from about 14 to about 39deciliters/gram. In most cases the intrinsic viscosity of the UHMWPE isin the range of from about 18 to about 39 deciliters/gram, typicallyfrom about 18 to about 32 deciliters/gram.

The nominal molecular weight of UHMWPE is empirically related to theintrinsic viscosity of the polymer according to the equation:

M(UHMWPE)=5.3×10⁴[η]^(1.37)

where M(UHMWPE) is the nominal molecular weight and [η] is the intrinsicviscosity of the UHMW polyethylene expressed in deciliters/gram.

As used herein and in the claims, intrinsic viscosity is determined byextrapolating to zero concentration the reduced viscosities or theinherent viscosities of several dilute solutions of the UHMWPE where thesolvent is freshly distilled decahydronaphthalene to which 0.2 percentby weight, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid,neopentanetetrayl ester [CAS Registry No. 6683-19-8] has been added. Thereduced viscosities or the inherent viscosities of the UHMWPE areascertained from relative viscosities obtained at 135° C. using anUbbelohde No. 1 viscometer in accordance with the general procedures ofASTM D 4020-81, except that several dilute solutions of differingconcentration are employed. ASTM D 4020-81 is, in its entirety,incorporated herein by reference.

In one particular embodiment, the matrix comprises a mixture ofsubstantially linear ultrahigh molecular weight polyethylene having anintrinsic viscosity of at least 10 deciliters/gram, and lower molecularweight polyethylene (LMWPE) having an ASTM D 1238-86 Condition E meltindex of less than 50 grams/10 minutes and an ASTM D 1238-86 Condition Fmelt index of at least 0.1 gram/10 minutes. The nominal molecular weightof LMWPE is lower than that of the UHMW polyethylene. LMWPE isthermoplastic and many different types are known. One method ofclassification is by density, expressed in grams/cubic centimeter androunded to the nearest thousandth, in accordance with ASTM D 1248-84(re-approved 1989), as summarized as follows:

Type Abbreviation Density (g/cm³) Low Density Polyethylene LDPE0.910-0.925 Medium Density Polyethylene MDPE 0.926-0.940 High DensityPolyethylene HDPE 0.941-0.965Any or all of these polyethylenes may be used as the LMWPE in thepresent invention. For some applications, HDPE may be used because itordinarily tends to be more linear than MDPE or LDPE. ASTM D 1248-84(Reapproved 1989) is, in its entirety, incorporated herein by reference.

Processes for making the various LMWPE's are well known and welldocumented. They include the high pressure process, the PhillipsPetroleum Company process, the Standard Oil Company (Indiana) process,and the Ziegler process.

The ASTM D 1238-86 Condition E (that is, 190° C. and 2.16 kilogram load)melt index of the LMWPE is less than about 50 grams/10 minutes. Oftenthe Condition E melt index is less than about 25 grams/10 minutes.Typically, the Condition E melt index is less than about 15 grams/10minutes.

The ASTM D 1238-86 Condition F (that is, 190° C. and 21.6 kilogram load)melt index of the LMWPE is at least 0.1 gram/10 minutes. In many casesthe Condition F melt index is at least about 0.5 gram/10 minutes.Typically, the Condition F melt index is at least about 1.0 gram/10minutes. ASTM D 1238-86 is, in its entirety, incorporated herein byreference.

Sufficient UHMWPE and LMWPE should be present in the matrix to providetheir properties to the microporous material. Other thermoplasticorganic polymers may also be present in the matrix so long as theirpresence does not materially affect the properties of the microporousmaterial in an adverse manner. One or more other thermoplastic polymersmay be present in the matrix. The amount of the other thermoplasticpolymer which may be present depends upon the nature of such polymer.Examples of thermoplastic organic polymers which may optionally bepresent include, but are not limited to, poly(tetrafluoroethylene),polypropylene, copolymers of ethylene and propylene, copolymers ofethylene and acrylic acid, and copolymers of ethylene and methacrylicacid. If desired, all or a portion of the carboxyl groups ofcarboxyl-containing copolymers may be neutralized with sodium, zinc, orthe like.

In most cases the UHMWPE and the LMWPE together constitute at leastabout 65 percent by weight of the polymer of the matrix. Often theUHMWPE and the LMWPE together constitute at least about 85 percent byweight of the polymer of the matrix. Typically, the other thermoplasticorganic polymers are substantially absent so that the UHMWPE and theLMWPE together constitute substantially 100 percent by weight of thepolymer of the matrix.

The UHMWPE can constitute at least one percent by weight of the polymerof the matrix. Where the UHMWPE and the LMWPE together constitute 100percent by weight of the polymer of the matrix of the microporousmaterial, the UHMWPE can constitute greater than or equal to 40 percentby weight of the polymer of the matrix, such as greater than or equal to45 percent by weight, or greater than or equal to 48 percent by weight,or greater than or equal to 50 percent by weight, or greater than orequal to 55 percent by weight of the polymer of the matrix. Also, theUHMWPE can constitute less than or equal to 99 percent by weight of thepolymer of the matrix, such as less than or equal to 80 percent byweight, or less than or equal to 70 percent by weight, or less than orequal to 65 percent by weight, or less than or equal to 60 percent byweight of the polymer of the matrix. The level of UHMWPE comprising thepolymer of the matrix can range between any of these values inclusive ofthe recited values.

Likewise, where the UHMWPE and the LMWPE together constitute 100 percentby weight of the polymer of the matrix of the microporous material, theLMWPE can constitute greater than or equal to 1 percent by weight of thepolymer of the matrix, such as greater than or equal to 5 percent byweight, or greater than or equal to 10 percent by weight, or greaterthan or equal to 15 percent by weight, or greater than or equal to 20percent by weight, or greater than or equal to 25 percent by weight, orgreater than or equal to 30 percent by weight, or greater than or equalto 35 percent by weight, or greater than or equal to 40 percent byweight, or greater than or equal to 45 percent by weight, or greaterthan or equal to 50 percent by weight, or greater than or equal to 55percent by weight of the polymer of the matrix. Also, the LMWPE canconstitute less than or equal to 70 percent by weight of the polymer ofthe matrix, such as less than or equal to 65 percent by weight, or lessthan or equal to 60 percent by weight, or less than or equal to 55percent by weight, or less than or equal to 50 percent by weight, orless than or equal to 45 percent by weight of the polymer of the matrix.The level of the LMWPE can range between any of these values inclusiveof the recited values.

It should be noted that for any of the previously described microporousmaterials of the present invention, the LMWPE can comprise high densitypolyethylene.

The microporous material also includes a finely-divided, substantiallywater-insoluble particulate filler material. The particulate fillermaterial may include an organic particulate material and/or an inorganicparticulate material. The particulate filler material typically is notcolored, for example, the particulate filler material is a white oroff-white particulate filler material, such as a siliceous or clayparticulate material.

The finely divided substantially water-insoluble filler particles mayconstitute from 20 to 90 percent by weight of the microporous material.For example, such filler particles may constitute from 30 percent to 90percent by weight of the microporous material, or from 40 to 90 percentby weight of the microporous material, or from 40 to 85, e.g., 45 to 80,percent by weight of the microporous material, or from 50 to 80, e.g.,50 to 65, 70 or 75, percent by weight of the microporous material andeven from 60 percent to 90 percent by weight of the microporousmaterial.

The finely divided substantially water-insoluble particulate filler maybe in the form of ultimate particles, aggregates of ultimate particles,or a combination of both. At least about 90 percent by weight of thefiller used in preparing the microporous material has gross particlesizes in the range of from 0.5 to about 200 micrometers, such as from 1to 100 micrometers, as determined by the use of a laser diffractionparticle size instrument, LS230 from Beckman Coulton, which is capableof measuring particle diameters as small as 0.04 micrometers. Typically,at least 90 percent by weight of the particulate filler has grossparticle sizes in the range of from 5 to 40, e.g., 10 to 30 micrometers.The sizes of the filler agglomerates may be reduced during processing ofthe ingredients used to prepare the microporous material. Accordingly,the distribution of gross particle sizes in the microporous material maybe smaller than in the raw filler itself.

Non-limiting examples of suitable organic and inorganic particulatematerials, that may be used in the microporous material of the presentinvention, include those described in U.S. Pat. No. 6,387,519 B1 atcolumn 9, line 4 to column 13, line 62, the cited portions of which areincorporated herein by reference.

In a particular embodiment of the present invention, the particulatefiller material comprises siliceous materials. Non-limiting examples ofsiliceous fillers that may be used to prepare the microporous materialinclude silica, mica, montmorillonite, kaolinite, nanoclays such ascloisite, which is available from Southern Clay Products, talc,diatomaceous earth, vermiculite, natural and synthetic zeolites, calciumsilicate, aluminum silicate, sodium aluminum silicate, aluminumpolysilicate, alumina silica gels and glass particles. In addition tothe siliceous fillers, other finely divided particulate substantiallywater-insoluble fillers optionally may also be employed. Non-limitingexamples of such optional particulate fillers include carbon black,charcoal, graphite, titanium oxide, iron oxide, copper oxide, zincoxide, antimony oxide, zirconia, magnesia, alumina, molybdenumdisulfide, zinc sulfide, barium sulfate, strontium sulfate, calciumcarbonate, and magnesium carbonate. Some of such optional fillers arecolor-producing fillers and, depending on the amount used, may add a hueor color to the microporous material. In a non-limiting embodiment, thesiliceous filler may include silica and any of the aforementioned clays.Non-limiting examples of silicas include precipitated silica, silicagel, fumed silica, and combinations thereof.

Silica gel is generally produced commercially by acidifying an aqueoussolution of a soluble metal silicate, e.g., sodium silicate, at low pHwith acid. The acid employed is generally a strong mineral acid such assulfuric acid or hydrochloric acid, although carbon dioxide can be used.Inasmuch as there is essentially no difference in density between thegel phase and the surrounding liquid phase while the viscosity is low,the gel phase does not settle out, that is to say, it does notprecipitate. Consequently, silica gel may he described as anon-precipitated, coherent, rigid, three-dimensional network ofcontiguous particles of colloidal amorphous silica. The state ofsubdivision ranges from large, solid masses to submicroscopic particles,and the degree of hydration from almost anhydrous silica to softgelatinous masses containing on the order of 100 parts of water per partof silica by weight.

Precipitated silica generally is produced commercially by combining anaqueous solution of a soluble metal silicate, ordinarily alkali metalsilicate such as sodium silicate, and an acid so that colloidalparticles of silica will grow in a weakly alkaline solution and becoagulated by the alkali metal ions of the resulting soluble alkalimetal salt. Various acids may be used, including but not limited tomineral acids. Non-limiting examples of acids that may be used includehydrochloric acid and sulfuric acid, but carbon dioxide can also be usedto produce precipitated silica. In the absence of a coagulant, silica isnot precipitated from solution at any pH. In a non-limiting embodiment,the coagulant used to effect precipitation of silica may be the solublealkali metal salt produced during formation of the colloidal silicaparticles, or it may be an added electrolyte, such as a solubleinorganic or organic salt, or it may be a combination of both.

Many different precipitated silicas can be employed as the siliceousfiller used to prepare the microporous material. Precipitated silicasare well-known commercial materials, and processes for producing themare described in detail in many United States Patents, including U.S.Pat. Nos. 2,940,830 and 4,681,750. The average ultimate particle size(irrespective of whether or not the ultimate particles are agglomerated)of precipitated silica used to prepare the microporous material isgenerally less than 0.1 micrometer, e.g., less than 0.05 micrometer orless than 0.03 micrometer, as determined by transmission electronmicroscopy. Precipitated silicas are available in many grades and formsfrom PPG Industries, Inc. These silicas are sold under the Hi-Sil®trademark.

For purposes of the present invention, the finely divided particulatesubstantially water-insoluble siliceous filler can comprise at least 50percent by weight, e.g., at least 65 or at least 75 percent by weight,or at least 90 percent by weight of the substantially water-insolublefiller material. The siliceous filler may comprise from 50 to 90 percentby weight, e.g., from 60 to 80 percent by weight, of the particulatefiller material, or the siliceous filler may comprise substantially allof the substantially water-insoluble particulate filler material.

The particulate filler, e.g., the siliceous filler, typically has a highsurface area, which allows the filler to carry much of the processingplasticizer composition used to produce the microporous material of thepresent invention. High surface area fillers are materials of very smallparticle size, materials that have a high degree of porosity, ormaterials that exhibit both of such properties. The surface area of theparticulate filler, e.g., the siliceous filler particles, can range from20 or 40 to 400 square meters per gram, e.g., from 25 to 350 squaremeters per gram, or from 40 to 160 square meters per gram, as determinedby the Brunauer, Emmett, Teller (BET) method according to ASTM D1993-91. The BET surface area is determined by fitting five relativepressure points from a nitrogen sorption isotherm measurement made usinga Micromeritics TriStar 3000™ instrument. A FlowPrep-060™ station can beused to provide heat and continuous gas flow during sample preparation.Prior to nitrogen sorption, silica samples are dried by heating to 160°C. in flowing nitrogen (PS) for 1 hour. Generally, but not necessarily,the surface area of any non-siliceous filler particles used is alsowithin one of these ranges. The filler particles are substantiallywater-insoluble and also can be substantially insoluble in any organicprocessing liquid used to prepare the microporous material. This canfacilitate retention of the particulate filler within the microporousmaterial.

The microporous material of the present may also include minor amounts,e.g., less than or equal to 5 percent by weight, based on total weightof the microporous material, of other materials used in processing, suchas lubricant, processing plasticizer, organic extraction liquid, water,and the like. Further materials introduced for particular purposes, suchas thermal, ultraviolet and dimensional stability, may optionally bepresent in the microporous material in small amounts, e.g., less than orequal to 15 percent by weight, based on total weight of the microporousmaterial. Examples of such further materials include, but are notlimited to, antioxidants, ultraviolet light absorbers, reinforcingfibers such as chopped glass fiber strand, and the like. The balance ofthe microporous material, exclusive of filler and any coating, printingink, or impregnant applied for one or more special purposes isessentially the thermoplastic organic polymer.

The microporous material of the present invention, also includes anetwork of interconnecting pores, which communicate substantiallythroughout the microporous material. On a coating-free, printing inkfree and impregnant-free basis, pores typically constitute from 35 to 95percent by volume, based on the total volume of the microporousmaterial, when made by the processes as further described herein. Thepores may constitute from 60 to 75 percent by volume of the microporousmaterial, based on the total volume of the microporous material. As usedherein and in the claims, the porosity (also known as void volume) ofthe microporous material, expressed as percent by volume, is determinedaccording to the following equation:

Porosity=100[1−d ₁ /d ₂]

where, d₁ is the density of the sample, which is determined from thesample weight and the sample volume as ascertained from measurements ofthe sample dimensions; and d₂ is the density of the solid portion of thesample, which is determined from the sample weight and the volume of thesolid portion of the sample. The volume of the solid portion of themicroporous material is determined using a Quantachrome stereopycnometer(Quantachrome Corp.) in accordance with the operating manualaccompanying the instrument.

The volume average diameter of the pores of the microporous material isdetermined by mercury porosimetry using an Autoscan mercury porosimeter(Quantachrome Corp.) in accordance with the operating manualaccompanying the instrument. The volume average pore radius for a singlescan is automatically determined by the porosimeter. In operating theporosimeter, a scan is made in the high pressure range (from 138kilopascals absolute to 227 megapascals absolute). If 2 percent or lessof the total intruded volume occurs at the low end (from 138 to 250kilopascals absolute) of the high pressure range, the volume averagepore diameter is taken as twice the volume average pore radiusdetermined by the porosimeter. Otherwise, an additional scan is made inthe low pressure range (from 7 to 165 kilopascals absolute) and thevolume average pore diameter is calculated according to the equation:

d=2 [v ₁ r ₁ /w ₁ +v ₂ r ₂ /w ₂ ]/[v ₁ /w ₁ +v ₂ /w ₂]

where, d is the volume average pore diameter; v₁ is the total volume ofmercury intruded in the high pressure range; v₂ is the total volume ofmercury intruded in the low pressure range; r₁ is the volume averagepore radius determined from the high pressure scan; r₂ is the volumeaverage pore radius determined from the low pressure scan; w₁ is theweight of the sample subjected to the high pressure scan; and w₂ is theweight of the sample subjected to the low pressure scan.

Generally on a coating-free, printing ink-free and impregnant-freebasis, the volume average diameter of the pores of the microporousmaterial is at least 0.02 micrometers, typically at least 0.04micrometers, and more typically at least 0.05 micrometers. On the samebasis, the volume average diameter of the pores of the microporousmaterial is also typically less than or equal to 0.5 micrometers, moretypically less than or equal to 0.3 micrometers, and further typicallyless than or equal to 0.25 micrometers. The volume average diameter ofthe pores, on this basis, may range between any of these values,inclusive of the recited values. For example, the volume averagediameter of the pores of the microporous material may range from 0.02 to0.5 micrometers, or from 0.04 to 0.3 micrometers, or from 0.05 to 0.25micrometers, in each case inclusive of the recited values.

In the course of determining the volume average pore diameter by meansof the above described procedure, the maximum pore radius detected mayalso be determined. This is taken from the low pressure range scan, ifrun; otherwise it is taken from the high pressure range scan. Themaximum pore diameter of the microporous material is typically twice themaximum pore radius.

Coating, printing and impregnation processes can result in filling atleast some of the pores of the microporous material. In addition, suchprocesses may also irreversibly compress the microporous material.Accordingly, the parameters with respect to porosity, volume averagediameter of the pores, and maximum pore diameter are determined for themicroporous material prior to application of one or more of theseprocesses.

Numerous art-recognized processes may be used to produce the microporousmaterials of the present invention. For example, the microporousmaterial of the present invention can be prepared by mixing togetherfiller particles, thermoplastic organic polymer powder, processingplasticizer and minor amounts of lubricant and antioxidant, until asubstantially uniform mixture is obtained. The weight ratio ofparticulate filler to polymer powder employed in forming the mixture isessentially the same as that of the microporous material to be produced.The mixture, together with additional processing plasticizer, istypically introduced into the heated barrel of a screw extruder.Attached to the terminal end of the extruder is a sheeting die. Acontinuous sheet formed by the die is forwarded without drawing to apair of heated calender rolls acting cooperatively to form a continuoussheet of lesser thickness than the continuous sheet exiting from thedie. The level of processing plasticizer present in the continuous sheetat this point in the process can vary and will effect the density of thefinal microporous sheet. For example, the level of processingplasticizer present in the continuous sheet, prior to extraction asdescribed herein below, can be greater than or equal to 30 percent byweight of the continuous sheet, such as greater than or equal to 40percent by weight, or greater than or equal to 45 percent by weight ofthe continuous sheet prior to extraction. Also, the amount of processingplasticizer present in the continuous sheet prior to extraction can beless than or equal to 70 percent by weight of the continuous sheet, suchas less than or equal to 65 percent by weight, or less than or equal to60 percent by weight, or less than or equal to 57 percent by weight ofthe continuous sheet prior to extraction. The level of processingplasticizer present in the continuous sheet at this point in theprocess, prior to extraction, can range between any of these valuesinclusive of the recited values. Generally, the level of processingplasticizer can in one embodiment vary from 57 to 62 weight percent, andin another embodiment be less than 57 weight percent.

The continuous sheet from the calender is then passed to a firstextraction zone where the processing plasticizer is substantiallyremoved by extraction with an organic liquid, which is a good solventfor the processing plasticizer, a poor solvent for the organic polymer,and more volatile than the processing plasticizer. Usually, but notnecessarily, both the processing plasticizer and the organic extractionliquid are substantially immiscible with water. The continuous sheetthen passes to a second extraction zone where residual organicextraction liquid is substantially removed by steam and/or water. Thecontinuous sheet is then passed through a forced air dryer forsubstantial removal of residual water and remaining residual organicextraction liquid. From the dryer the continuous sheet, which ismicroporous material, is passed to a take-up roll.

The processing plasticizer is a liquid at room temperature and usuallyis a processing oil such as paraffinic oil, naphthenic oil, or aromaticoil. Suitable processing oils include those meeting the requirements ofASTM D 2226-82, Types 103 and 104. More typically, processing oilshaving a pour point of less than 220° C. according to ASTM D 97-66(re-approved 1978) are used to produce the microporous material of thepresent invention. Processing plasticizers useful in preparing themicroporous material of the present invention are discussed in furtherdetail in U.S. Pat. No. 5,326,391 at column 10, lines 26 through 50,which disclosure is incorporated herein by reference.

In an embodiment of the present invention, the processing plasticizercomposition used to prepare the microporous material has littlesolvating effect on the polyolefin at 60° C., and only a moderatesolvating effect at elevated temperatures on the order of 100° C. Theprocessing plasticizer composition generally is a liquid at roomtemperature. Non-limiting examples of processing oils that may be usedcan include SHELLFLEX® 412 oil, SHELLFLEX® 371 oil (Shell Oil Co.),which are solvent refined and hydrotreated oils derived from naphtheniccrude oils, ARCOprime® 400 oil (Atlantic Richfield Co.) and KAYDOL® oil(Witco Corp.), which are white mineral oils. Other non-limiting examplesof processing plasticizers can include phthalate ester plasticizers,such as dibutyl phthalate, bis(2-ethylhexyl) phthalate, diisodecylphthalate, dicyclohexyl phthalate, butyl benzyl phthalate, andditridecyl phthalate. Mixtures of any of the foregoing processingplasticizers can be used to prepare the microporous material of thepresent invention.

There are many organic extraction liquids that can be used to preparethe microporous material of the present invention. Examples of suitableorganic extraction liquids include those described in U.S. Pat. No.5,326,391 at column 10, lines 51 through 57, which disclosure isincorporated herein by reference.

The extraction fluid composition can comprise halogenated hydrocarbons,such as chlorinated hydrocarbons and/or fluorinated hydrocarbons. Inparticular, the extraction fluid composition may include halogenatedhydrocarbon(s) and have a calculated solubility parameter coulomb term(δclb) ranging from 4 to 9 (Jcm³)^(1/2). Non-limiting examples ofhalogenated hydrocarbon(s) suitable as the extraction fluid compositionfor use in producing the microporous material of the present inventioncan include one or more azeotropes of halogenated hydrocarbons selectedfrom trans-1,2-dichloroethylene, 1,1,1,2,2,3,4,5,5,5-decafluoropentane,and/or 1,1,1,3,3-pentafluorobutane. Such materials are availablecommercially as VERTREL MCA (a binary azeotrope of1,1,1,2,2,3,4,5,5,5-dihydrodecafluoropentane andtrans-1,2-dichloroethylene: 62%/38%), and VERTREL CCA (a ternaryazeotrope of 1,1,1,2,2,3,4,5,5,5-dihydrodecafluorpentane, 1,1,1,3,3-pentafluorbutane, and trans-1,2-dichloroethylene: 33%/28%/39%),both available from MicroCare Corporation.

The residual processing plasticizer content of microporous materialaccording to the present invention is usually less than 10 percent byweight, based on the total weight of the microporous material, and thisamount may be further reduced by additional extractions using the sameor a different organic extraction liquid. Often the residual processingplasticizer content is less than 5 percent by weight, based on the totalweight of the microporous material, and this amount may be furtherreduced by additional extractions.

The microporous material of the present invention may also be producedaccording to the general principles and procedures of U.S. Pat. Nos.2,772,322; 3,696,061; and/or 3,862,030. These principles and proceduresare particularly applicable where the polymer of the matrix is or ispredominately poly(vinyl chloride) or a copolymer containing a largeproportion of polymerized vinyl chloride.

Microporous materials produced by the above-described processesoptionally may be stretched. Stretching of the microporous materialtypically results in both an increase in the void volume of thematerial, and the formation of regions of increased or enhancedmolecular orientation. As is known in the art, many of the physicalproperties of molecularly oriented thermoplastic organic polymer,including tensile strength, tensile modulus, Young's modulus, andothers, differ, e.g., considerably, from those of the correspondingthermoplastic organic polymer having little or no molecular orientation.Stretching is typically accomplished after substantial removal of theprocessing plasticizer as described above.

Various types of stretching apparatus and processes are well known tothose of ordinary skill in the art, and may be used to accomplishstretching of the microporous material of the present invention.Stretching of the microporous materials is described in further detailin U.S. Pat. No. 5,326,391 at column 11, line 45 through column 13, line13, which disclosure is incorporated herein by reference.

The present invention is more particularly described in the examplesthat follow, which are intended to be illustrative only, since numerousmodifications and variations therein will be apparent to those skilledin the art. Unless otherwise specified, all parts and percentages are byweight.

EXAMPLES

In Part 1 of the following examples, the materials and methods used toprepare the Example and Comparative mixes prepared in the pilot plantand presented in Table 1 and the Example mixes prepared in the scale-upprocess and Comparative commercial samples presented in Table 2 aredescribed. In Part 2, the methods used to extrude, calender and extractthe sheets prepared from the mixes of Part 1 and Part 2 are described.In Part 3, the methods used to determine the physical propertiesreported in Tables 3 and 4 are described. In Parts 4A and 4B, thecoating formulations used are listed in Tables 5 and 7 and theproperties of the coated sheets are listed in Tables 6 and 8. In Part 5,The Benzyl Acetate Test results for the products of Tables 1, 2, 6 and 8are listed in Tables 9, 10, 11 and 12.

Part 1—Mix Preparation

The dry ingredients were weighed into a FM-130D Littleford plough blademixer with one high intensity chopper style mixing blade in the orderand amounts (grams (g) specified in Table I. The dry ingredients werepremixed for 15 seconds using the plough blades only. The process oil(Mix Oil) was then pumped in via a hand pump through a spray nozzle atthe top of the mixer, with only the plough blades running. The pumpingtime for the examples varied between 45-60 seconds. The high intensitychopper blade was turned on, along with the plough blades, and the mixwas mixed for 30 seconds. The mixer was shut off and the internal sidesof the mixer were scrapped down to insure all ingredients were evenlymixed. The mixer was turned back on with both high intensity chopper andplough blades turned on, and the mix was mixed for an additional 30seconds. The mixer was turned off and the mix dumped into a storagecontainer.

TABLE 1 Samples Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 11CE 1 CE 2 CE 3 CE 4 CE 5 Silica HiSil 1393 1393 1393 1393 0 0 1814 18141814 1393 1393 2270 2270 2270 135 (a) Ca Silicate 0.0 0.0 0.0 0.0 18161816 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (b) CaCO₃ (c) 544.3 544.3 544.3544.3 709.0 709.0 0.0 0.0 0.0 544.3 544.3 0.0 0.0 0.0 TiO₂(d) 90.7 90.790.7 90.7 118.0 118.0 87.3 87.3 87.3 90.7 90.7 91.0 91.0 91.0 UHMWPE515.3 515.3 515.3 515.3 581.0 671.0 592.0 592.0 592.0 515.3 515.3 560.0285.0 654.0 (e) HDPE (f) 475.4 475.4 475.4 475.4 710.0 619.0 129.0 0.00.0 475.4 475.4 560.0 654.0 654.0 LDPE (g) 0.0 0.0 0.0 0.0 0.0 0.0 664.5793.5 793.5 0.0 0.0 0.0 0.0 0.0 Antioxidant 14.5 14.5 14.5 14.5 18.918.9 20.1 20.1 20.1 14,5 14.5 7.7 7.7 7.7 (h) Lubricant (i) 14.5 14.514.5 14.5 18.9 18.9 21.6 21.6 21.6 14.5 14.5 22.7 22.7 22.7 Poly- 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 185.0 370.0 0.0 propylene (j)CFA (k) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 194.7Nanoclay 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 194.7 MB(l) Mix oil (m) 2841 2841 2841 2841 931 885 2836 2836 2836 2841 28413655 3851 3850 Process 47.8% 48.0% 49.8% 52.6% 47.8% 47.2% 53.3% 56.0%52.4% 55.9% 57.4% 60.5% 59.6% 57.7% Oil (%) (a) HI-SIL ® 135precipitated silica from PPG Industries, Inc. (b) INHIBISIL75precipitated calcium silicate from PPG Industries, Inc. (c) Calciumcarbonate from Camel White (d) TIPURE ® R-103 titanium dioxide from E.I.du Pont de Nemours and Company (e) GUR ® 4130 Ultra High MolecularWeight Polyethylene (UHMWPE), from Ticona Corp. (f) FINA ® 1288 HighDensity Polyethylene (HDPE), from Total Petrochemicals (g) Petrothene ®NA206000 LDPE from Lyondell Basel (h) CYANOX ® 1790 antioxidant fromCytec Industries, Inc. (i) Calcium stearate lubricant, technical grade(j) Used was PRO-FAX ® 7523 Polypropylene Copolymer from AshlandDistribution. (k) Foam PE MB, a chemical foaming agent from AmacetCorporation (l) NanoMax ® HDPE materbatch nanoclay from Nanocor (m)Tufflo ® 6056 process oil from PPC Lubricants

Scale-up Examples 10-18 were prepared in a plant scale-up batch sizeusing production scale equipment similar to the equipment and proceduresdescribed above. The scale-up samples were prepared from a mix ofingredients listed in Table 2 as the weight percent of the total mix.

TABLE 2 Ingredients Ex. 10 Ex. 11 Ex. 12 Ex 13 Ex. 14 Ex. 15 Ex. 16 Ex.17 Ex. 18 HiSil ® 135 (a) 23.66 23.66 23.66 23.66 24.77 24.77 24.7724.77 24.77 CaCO₃ (c) 9.24 9.24 9.24 9.24 9.68 9.68 9.68 9.68 9.68 TiO₂(d) 1.54 1.54 1.54 1.54 1.61 1.61 1.61 1.61 1.61 UHMWPE (e) 8.75 8.758.75 8.75 9.16 9.16 9.16 8.45 8.45 HDPE (f) 8.07 8.07 8.07 8.07 8.458.45 8.45 9.16 9.16 Antioxidant (h) 0.25 0.25 0.25 0.25 0.26 0.26 0.260.26 0.26 Lubricant (i) 0.25 0.25 0.25 0.25 0.26 0.26 0.26 0.26 0.26 MixOil (m) 48.24 48.24 48.24 48.24 45.81 45.81 45.81 45.81 45.81

Part 2—Extrusion, Calendering and Extraction

The mixes of the Examples 1-9 and Comparative Examples 1-5 were extrudedand calendered into final sheet form using an extrusion system includinga feeding, extrusion and calendering system described as follows. Agravimetric loss in weight feed system (K-tron model #K2MLT35D5) wasused to feed each of the respective mixes into a 27 mm twin screwextruder (model # was Leistritz Micro-27gg). The extruder barrel wascomprised of eight temperature zones and a heated adaptor to the sheetdie. The extrusion mixture feed port was located just prior to the firsttemperature zone. An atmospheric vent was located in the thirdtemperature zone. A vacuum vent was located in the seventh temperaturezone.

The mix was fed into the extruder at a rate of 90 g/minute. Variousamounts of additional processing oil also was injected at the firsttemperature zone, as required, to achieve the desired total oil contentin the extruded sheet. The oil contained in the extruded sheet(extrudate) being discharged from the extruder is referenced herein asthe “extrudate oil” or “process oil”, and is reported in weightpercentin Table 1, based on the total weight of the extruded sheet. Inaccordance with an embodiment of the present invention, densities ofgreater than 0.8 g/cm³ of the microporous sheet are obtained when theamount of process oil (extrudate oil) in the extruded sheet is less than57 weight percent. While not wishing to be bound by any particulartheory, it is believed from the experimental evidence at hand thatlowering the amount of process oil in the extruded microporous sheetincreases the density of the microporous sheet, e.g., to greater than0.8 g/cm³ and alters the surface of the sheet so that volatile materialtransferred to the vapor release surface is more dispersed and does notpool initially into droplets on that surface.

Extrudate from the barrel was discharged into a 15-centimeter wide sheetMasterflex® die having a 1.5 millimeter discharge opening. The extrusionmelt temperature was 203-210° C. and the throughput was 7.5 kilogramsper hour.

The calendering process was accomplished using a three-roll verticalcalender stack with one nip point and one cooling roll. Each of therolls had a chrome surface. Roll dimensions were approximately 41 cm inlength and 14 cm in diameter. The top roll temperature was maintainedbetween 135° C. to 140° C. The middle roll temperature was maintainedbetween 140° C. to 145° C. The bottom roll was a cooling roll whereinthe temperature was maintained between 10-21° C. The extrudate wascalendered into sheet form and passed over the bottom water cooled rolland wound up.

A sample of sheet cut to a width up to 25.4 cm and length of 305 cm wasrolled up and placed in a canister and exposed to hot liquid1,1,2-trichloroethylene for approximately 7-8 hours to extract oil fromthe sheet sample. Afterwards, the extracted sheet was air dried andsubjected to test methods described hereinafter.

The mixes of the Scale-up Examples 10-18, as shown in Table 2, wereextruded and calendered into final sheet form using an extrusion systemand oil extraction process that was a production sized version of thesystem described above, carried out as described in U.S. Pat. No.5,196,262, at column 7, line 52, to column 8, line 47, which descriptionis incorporated herein by reference. The final sheets were tested forphysical parameters using the test methods described above in Part 3.Comparative Examples 6-10 were commercial microporous productsidentified as follows: CE 6 was TESLIN® Digital 10 mil; CE 7 was Teslin®SP 6 mil; CE 8 was TESLIN® SP 10 mil; CE 9 was TESLIN® SP 14 mil; and CE10 was TESLIN® SP 12 mil.

The extrudate oil (weight percent) for the commercial products used forcomparative examples 6-10 varied from 57 to 62 percent.

Part 3—Testing and Results

Physical properties measured on the extracted and dried films and theresults obtained are listed in Tables 3 and 4. The extrudate oil weightpercent was measured using a Soxhlet extractor. The extrudate oil weightpercent determination used a specimen of extrudate sheet with no priorextraction. A sample specimen approximately 2.25 inches×5 inches (5.72cm×12.7 cm) was weighed and recorded to four decimal places. Eachspecimen was then rolled into a cylinder and placed into a Soxhletextraction apparatus and extracted for approximately 30 minutes usingtrichloroethylene (TCE) as the solvent. The specimens were then removedand dried. The extracted and dried specimens were then weighed. The oilweight percentage values (extrudate) were calculated as follows:

Oil Wt. %=(initial wt.−extracted wt.)×100/initial wt.

Thickness was determined using an Ono Sokki thickness gauge EG-225. Two4.5 inches×5 inch (11.43 cm×12.7 cm) specimens were cut from each sampleand the thickness for each specimen was measured in nine places (atleast ¾ of an inch (1.91 cm) from any edge). The arithmetic average ofthe readings was recorded in mils to 2 decimal places and converted tomicrons.

The density of the above-described examples was determined by dividingthe average anhydrous weight of two specimens measuring 4.5 inches×5inches (11.43 cm×12.7 cm) that were cut from each sample by the averagevolume of those specimens. The average volume was determined by boilingthe two specimens in deionized water for 10 minutes, removing andplacing the two specimens in room temperature deionized water, weighingeach specimen suspended in deionized water after it has equilibrated toroom temperature and weighing each specimen again in air after thesurface water was blotted off. The average volume of the specimens wascalculated as follows:

Volume(avg.)=[(weight of lightly blotted specimens weighed in air−sum ofimmersed weights)×1.002]/2

The anhydrous weight was determined by weighing each of the twospecimens on an analytical balance and multiplying that weight by 0.98since it was assumed that the specimens contained 2 percent moisture.

The Porosity reported in Tables 3 and 4 was determined using a Gurleydensometer, model 4340, manufactured by GPI Gurley Precision Instrumentsof Troy, N.Y. The Porosity reported was a measure of the rate of airflow through a sample or it's resistance to an air flow through thesample. The unit of measure is a “Gurley second” and represents the timein seconds to pass 100 cc of air through a 1 inch square (6.4×10⁻⁴ m²)area using a pressure differential of 4.88 inches of water (12.2×10²Pa). Lower values equate to less air flow resistance (more air isallowed to pass freely). The measurements were completed using theprocedure listed in the manual, MODEL 4340 Automatic Densometer andSmoothness Tester Instruction Manual. TAPPI method T 460 om-06-AirResistance of Paper can also be referenced for the basic principles ofthe measurement.

TABLE 3 Property Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9CE 1 CE 2 CE 3 CE 4 CE 5 Sheet 262 264 264 262 371 419 173 155 173 260246 174 160 169 Thickness (μm) Extrudate 47.8% 48.0% 49.8% 52.6% 47.8%47.2% 53.5% 56.0% 52.4% 55.9% 57.4% 60.5% 59.6% 57.7% Oil wt. % Density0.764 0.828 0.755 0.707 0.892 0.901 0.646 0.612 0.701 0.750 0.695 0.5840.659 0.620 (g/cc) Porosity 2148 2161 2009 1988 1685 1730 3787 3735 41551842 1517 1473 1309 1410 (Gurley Sec.)

TABLE 4 Property Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17Ex. 18 CE 6 CE 7 CE 8 CE 9 CE 10 Sheet 291 293 269 286 289 288 278 277284 284 157 250 359 306 Thickness (μm) Extrudate 58.0% 57.6% 58.0% 57.1%55.0% 53.5% 54.0% 54.0% 53.0% — — — — — Oil wt % Density 0.795 0.8040.809 0.815 0.818 0.882 0.835 0.835 0.862 0.719 0.607 0.677 0.691 0.672(g/cc) Porosity 2877 3017 3395 3208 2800 2872 3048 2849 3102 5983 18673659 4110 4452 (Gurley Sec.)

Part 4A—Coating Formulations and Coated Products

Coatings 1-5 listed in Table 5 were prepared by dispersing CELVOL® 325polyvinyl alcohol in cool water under mild agitation in a 600 mL beaker.Mild agitation was provided with a 1″ (2.54 cm) paddle stirrer driven byan electric stir motor. The mixture was heated to 190° F. (87.8° C.) andstirred for 20-30 minutes. The resultant solution was allowed to cool toroom temperature while stirring. Specific mix amounts and resultantmeasured solids are outlined in Table 5.

TABLE 5 Coating Formulations CELVOL ® 325, Deionized water, MeasuredSolids, Coating # (grams) (grams) % by weight 1 7.5 292.5 2.5 ± 0.3 211.3 288.7 3.8 ± 0.3 3 13.5 286.5 4.5 ± 0.3 4 18.0 282.0 6.0 ± 0.3 515.0 285.0 5.0 ± 0.3

The coatings, confirmed to be free of visible undissolved particles,were applied to TESLIN® HD microporous substrate sold by PPG Industries,Pittsburgh, Pa. The coatings were applied to sheets of 8.5 inches×11inches, (21.59 cm×27.94 cm) 11 mils thick substrate each of which hadbeen tare on a balance prior to placing the sheet on a clean glasssurface and using tape to adhere the top corners of the sheet to theglass. A piece of clear 10 mil thick polyester 11 inches×3 inches (27.94cm×7.62 cm) was positioned across the top edge of the sheet, covering ½inch (1.27 cm) down from the top edge of the sheet. The polyester wasfixed to the glass surface with tape. A wire wrapped metering rod fromDiversified Enterprises was placed 1-2 inches (2.5-5.1 cm) above thesheet, parallel to the top edge, near the top edge of the polyester. A10-20 mL quantity of coating was deposited as a bead strip(approximately ¼ inch (0.64 cm) wide) directly next to and touching themetering rod using a disposable pipette. The bar was drawn completelyacross the sheet, attempting a continuous/constant rate. The resultantwet sheet was removed from the glass surface, immediately placed on thepreviously tare balance, weighed, the wet coating weight recorded thenthe coated sheet was placed in a forced air oven and dried at 95° C. for2 minutes. The dried sheet was removed from the oven and the samecoating procedure was repeated to the same coated sheet surface. The twowet coating weights were used to calculate the final dry coat weight ingrams per square meter. The coated sheets of Examples 19-23 aredescribed in Table 6.

TABLE 6 Final Coated Sheets Ex- 1^(st) Wet 2^(nd) Wet Total wetCalculated am- Coating Wire Coat Coat coating Final Coat ple Solids,Wrapped Weight, Weight, weight, Weight, # % Rod # grams grams grams gsm19 2.5 3 0.6 0.65 1.25  0.5 ± 0.1 20 3.8 3 0.61 0.59 1.20 0.75 ± 0.1 214.5 3 0.70 0.64 1.34  1.0 ± 0.2 22 6 3 0.76 0.64 1.40  1.5 ± 0.1 23 5 101.18 1.20 2.38  2.1 ± 0.2

The following formula was used to calculate the final dry coat weight.

Calculated Final Dry Coat Weight in grams per square meter=((coatingssolids×0.01)×(1^(st) wet coating wgt.+2^(nd) wet coatingwgt.))/(8.5×10.5)×1550

Part 4B—Coating Formulations and Coated Products

The procedure of Part 4A was followed in preparing the coatingformulations of Coatings 6-12, except that Coating 7 was mixed for 2days prior to use. The coating formulations are listed in Table 7.

The substrate used in this Part 4B was TESLIN® SP1000 microporoussubstrate sold by PPG Industries, Pittsburgh, Pa. The same procedureused in Part 4A was followed except that some sheets were coated on bothsides, drying the first coated side prior to applying the second on theopposite side and a number 9 metering rod was used for all of thecoatings. Information on the final coated sheets is included in Table 8.

TABLE 7 Coating Formulations with amounts listed in grams Ingredients 67 8 9 10 11 12 Witcobond W240_((n)) 8 8 8 8 16 0 0 Aerosil ® 200_((o))2.5 0 0 0 0 0 0 CaCO_(3(c)) 0 2.5 0 0 0 0 0 HiSil ® T 700_((p)) 0 0 2.50 0 0 0 Lo-Vel ® 6200_((q)) 0 0 0 2.5 0 0 0 MOMENTIVE LE-410_((r)) 0 0 00 0 0.54 0 HYCAR 26138_((s)) 0 0 0 0 0 0 10 Deionized Water 39.5 39.539.5 39.5 34.0 49.5 40 Total, grams 50 50 50 50 50 50 50 Solids, % 10 1010 10 10 0.4 10 _((n))WITCOBOND W-240, an aqueous polyurethanedispersion from Chemtura Corporation. _((o))Aerosil ® 200 fumed silicafrom Degussa. _((p))HiSil ® T700 precipitated silica from PPGIndustries, Inc. _((q))Lo-Vel ® 6200 precipitated silica from PPGIndustries, Inc. _((r))MOMENTIVE LE-410 an aqueous silicon dispersionfrom Momentive Performance Materials. _((s))HYCAR 26138, an aqueouspoly(meth)acrylate dispersion from Lubrizol Advanced Materials, Inc.

TABLE 8 Final Coated Sheets Wet Coating weight Final Coating Example #Coating # Coating Type (grams weight (gsm) 24 10 Single 0.95 1.7 25 10Both Sides 2.0 3.5 26 11 Both Sides 2.0 0.14 27 12 Both Sides 2.1 3.9 CE11 11 Single 0.9 0.07 CE 12 12 Single 1.1 1.9 CE 13 6 Both Sides 2.2 3.8CE 14 7 Both Sides 2.5 4.4 CE 15 8 Both Sides 2.3 3.9 CE 16 9 Both Sides2.3 4.0

Part 5—Benzyl Acetate Testing

The holder assembly used for evaporation rate and performance testing ofa membrane consisted of a front clamp with a ring gasket, a back clamp,test reservoir cup and four screws. The test reservoir cup wasfabricated from a clear thermoplastic polymer, having interiordimensions defined by a circular diameter at the edge of the open faceof approximately 4 centimeters and a depth of no greater than 1centimeter. The open face was used to determine the volatile materialtransfer rate.

Each clamp of the holder assembly had a 1.5 inch (3.8 cm) diametercircular opening to accommodate the test reservoir cup and provide anopening to expose the membrane under test. When placing a membrane undertest, i.e., a sheet of microporous material having a thickness of from 6to 18 mils, the back clamp of the holder assembly was placed on top of acork ring. The test reservoir cup was placed in the back clamp andcharged with approximately 2 mL of benzyl acetate. An approximately 2inch (5.1 cm) diameter disk was cut out of the membrane sheet and placeddirectly over and in contact with the edge of the reservoir cup suchthat 12.5 cm² of the volatile material contact surface of themicroporous sheet was exposed to the interior of the reservoir.

The front clamp of the holder was carefully placed over the entireassembly, with the screw holes aligned and so as not to disturb themembrane disk. When a coated microporous sheet was used, the coatedsurface was placed either toward the reservoir or toward the atmosphereas indicated in the Table below. The screws were attached and tightenedenough to prevent leaking. The ring gasket created a seal. The holderwas labeled to identify the membrane sample under test. From 5 to 10replicates were prepared for each test. Five replicates of a Control(uncoated sample) was included for the coated Examples. For the Examplesin Table 11, there were 5 Controls for each Example and the averageevaporation rate for each Control was reported with the correspondingExample as well as the percent reduction in evaporation rate of theexample compared to the corresponding Control. The coated surface ofExample 19-23 in Table 11 was towards the atmosphere.

Each holder assembly was weighed to obtain an initial weight of theentire charged assembly. The assembly was then placed, standing upright,in a laboratory chemical fume hood having approximate dimensions of 5feet [1.52 meters] (height)×5 feet [1.52 meters] (width)×2 feet [0.61meters] (depth). With the test reservoir standing upright, benzylacetate was in direct contact with at least a portion of the volatilematerial contact surface of the microporous sheet. The glass doors ofthe fume hood were pulled down, and the air flow through the hood wasadjusted so as to have eight (8) turns (or turnovers) of hood volume perhour. Unless otherwise indicated, the temperature in the hood wasmaintained at 25° C.±5° C. The humidity within in the fume hood wasambient. The test reservoirs were regularly weighed in the hood. Testingwas performed for five (5) days. The calculated weight loss of benzylacetate, in combination with the elapsed time and surface area of themicroporous sheet exposed to the interior of the test reservoir, wereused to determine the volatile material transfer rate of the microporoussheet, in units of mg/(hour*cm²). The average evaporation rate (mg/hr)of the replicates was reported for the entire assembly in the Tablesbelow. These two values are related by the following formula:

Average evaporation rate(mg/hr)/12.5 cm²=Volatile Material transferrate(mg/hour*cm²)

Marginal (Marg.) indicates that there were both passing and failingreplicates, or that the test had no failures as described by “pooling”and “dripping” of the benzyl acetate down the surface of the membrane,but had some drops of benzyl acetate forming beads on the surface of themembrane, which was also deemed unacceptable vis-à-vis, to be graded asa “pass” result. There is, however, a clear performance distinctionbetween a failing (FAIL) test result and a marginal (Marg.) test result,the latter being clearly superior, as discussed herein.

The date of Tables 2, 4 and 10 for Examples 10-18 and ComparativeExamples 6-10, which illustrate microporous sheets produced onproduction scale equipment, confirm the correlation between increasedsheet density, which is achieved by lowering the amount of extrudate oilin the extruded sheet, and passing of the benzyl acetate test. This datais summarized in Table 13.

TABLE 9 Samples Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 CE1 CE 2 CE 3 CE 4 CE 5 5 Day Pass Pass Pass Pass Pass Pass Pass Pass PassFail Fail Fail Fail Fail Results Evaporation 2.8 2.8 2.6 2.8 2.7 4.3 3.23.3 3.2 3.0 3.1 2.9 2.6 2.8 rate

TABLE 10 Samples Ex. 10 Ex. 11 Ex. 12 Ex 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17Ex. 18 CE 6 CE 7 CE 8 CE 9 CE 10 5 Day Marg. Marg. Marg. Marg. Pass PassPass Pass Pass Fail Fail Fail Fail Fail Results Evaporation 3.4 3.3 3.23.2 3.7 3.9 3.7 3.8 3.7 2.9 3.0 3.0 3.3 3.1 Rate

TABLE 11 Samples Ex. 19 Control Ex. 20 Control Ex. 21 Control Ex. 22Control Ex. 23 Control 5 Day Results Pass Fail Pass Fail Pass Fail PassFail Pass Fail Evaporation rate 4.09 4.65 3.61 4.69 2.05 4.10 2.68 4.691.25 4.03 Percent Reduction in 12 23 50 46 69 Evaporation Rate

TABLE 12 Ex. 24 Ex. 24 Ex. Ex. Ex. CE 11 CE 12 CE CE CE CE SamplesControl ⁽¹⁾ Ctr⁽²⁾ Cta⁽³⁾ 25 Control ⁽⁴⁾ 26 27 Cta⁽³⁾ Cta⁽³⁾ 13 14 15 165 Day Results Fail Pass Pass Pass Fail Pass Pass Fail Fail Fail FailFail Fail Evaporation 2.64 2.64 2.61 2.83 3.4 3.3 3.4 3.3 3.2 2.64 2.632.56 2.65 Rate ⁽¹⁾ Control of uncoated TESLIN ® HD microporous materialthat was included with Examples 24, 25, CE 13-16. ⁽²⁾Coated surface wasdirected toward reservoir of volatile material. ⁽³⁾Coated surface wasdirected toward the atmosphere. ⁽⁴⁾ Control of uncoated TESLIN ® HDmicroporous material that was included with Examples 26, 27, CE 11-12.

TABLE 13 Benzyl Acetate Sheet Density, Extrudate Oil, Example Set TestResult g/cc weight % Ex. 14-18 Pass 0.818-0.882 53-55 Ex. 10-13 Marginal0.795-0.815 57-58 CE 6-10 Fail 0.607-0.719 57-62

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A vapor permeable microporous materialcomprising: (a) a matrix of substantially water-insoluble thermoplasticorganic polymer comprising polyolefin; (b) finely divided, substantiallywater-insoluble particulate filler, said particulate filler beingdistributed throughout said matrix and constituting from 40 to 90percent by weight, based on the total weight of said microporousmaterial; and (c) a network of interconnecting pores communicatingsubstantially throughout said microporous material; wherein saidmicroporous material has, (1) a density of less than 0.8 g/cm³, (2) avolatile material contact surface and a vapor release surface, saidvolatile material contact surface and said vapor release surface beingsubstantially opposed to each other, and (3) a volatile materialtransfer rate, from said volatile material contact surface to said vaporrelease surface of from 0.04 to 0.6 mg/(hour*cm²) when the volatilematerial contact surface of the vapor permeable microporous material isplaced in contact with a volatile material and said vapor releasesurface is not in direct contact with the volatile material, and wherein(i) at least a portion of said volatile material contact surface has afirst coating thereon, and/or (ii) at least a portion of said vaporrelease surface has a second coating thereon, said first coating andsaid second coating each independently being formed from an aqueouscoating composition selected from the group consisting of aqueouspoly(meth)acrylate dispersions, aqueous polyurethane dispersions,aqueous silicon oil dispersions, and combinations thereof, and whenvolatile material is transferred from said volatile material contactsurface to said vapor release surface, said vapor release surface issubstantially free of liquid volatile material.
 2. The microporousmaterial of claim 1, wherein said microporous material has a density offrom 0.4 g/cm³ to less than 0.8 g/cm³.
 3. The microporous material ofclaim 1, wherein said microporous material has a density of from 0.4g/cm³ to 0.7 g/cm³.
 4. The microporous material of claim 1, wherein saidvolatile material transfer rate is from 0.30 to 0.55 mg/(hour*cm²). 5.The microporous material of claim 1, wherein the particles of thedispersion of each aqueous coating composition has a particle size offrom 200 to 400 nm.
 6. The microporous material of claim 5, wherein saidfirst coating and said second coating each independently have a coatingweight of from 0.1 to 3 g/m².
 7. The microporous material of claim 1,wherein said polyolefin comprises ultrahigh molecular weightpolyethylene having an intrinsic viscosity of at least 10deciliters/gram.
 8. The microporous material of claim 7, wherein saidultrahigh molecular weight polyolefin is ultrahigh molecular weightpolyethylene having an intrinsic viscosity of at least 18deciliters/gram.
 9. The microporous material of claim 8, wherein saidultrahigh molecular weight polyethylene has an intrinsic viscosity inthe range of from 18 to 39 deciliters/gram.
 10. The microporous materialof claim 1, wherein said matrix comprises a mixture of substantiallylinear ultrahigh molecular weight polyethylene having an intrinsicviscosity of at least 10 deciliters/gram and lower molecular weightpolyethylene having an ASTM D 1238-86 Condition E melt index of lessthan 50 grams/10 minutes and an ASTM D 1238-86 Condition F melt index ofat least 0.1 grams/10 minutes.
 11. The microporous material of claim 10,wherein said substantially linear ultrahigh molecular weightpolyethylene constitutes at least one percent by weight of said matrixand said substantially linear ultrahigh molecular weight polyethyleneand said lower molecular weight polyethylene together constitutesubstantially 100 percent by weight of the polymer of the matrix. 12.The microporous material of claim 11, wherein said lower molecularweight polyethylene is high density polyethylene.
 13. The microporousmaterial of claim 1, wherein said particulate filler comprises siliceousparticles comprising particulate silica.
 14. The microporous material ofclaim 13, wherein said particulate silica comprises particulateprecipitated silica.
 15. The microporous material of claim 1, whereinsaid pores constitute from 35 to 95 percent by volume of saidmicroporous material, based on the total volume of said microporousmaterial.